Fuelish Tendencies

How To Correctly Set Up Your Fuel System

A fuel system is just that---a system! All the pieces and components must work together. The current trend is to run a pump that provides considerably more volume than should be required to compensate for deficiencies within the system. Simply buying and installing the biggest pump you can find will not be adequate if the rest of the system is poorly designed or sloppily implemented. The same is true when prurchasing a fuel pump based upon price, or by what someone believes is enough fuel pump for the application. Either deficiency can easily drain the wallet if you run out of fuel and start damaging expenisive internal engine components ... not to mention losing races!

This article will focus on electric fuel pumps. Mechanical fuel pumps are not worth the effort unless mandated by the rules of a specific class (as in many circle track applications) to run one. Use the same basic knowledge provided here with a mechanical fuel pump in regards to requirements and fuel regulator choices.

Fuel pumps are generally rated in gallons per hour (or GPH). Mallory, for example, offers pumps rated at 70, 110, 140, and 250 GPH. All of the Mallory pumps are of gerotor type which makes them quieter and sometimes more efficient than rotary, vane style pumps. However, it is mandatory that a fuel filter be installed between the fuel cell (or tank) and the pump. The higher efficiency of the gerotor pump is also less tolerant of garbage getting into it. It should be stated that a best practice is to always run a filter before the fuel pump, no matter the design! A quality, properly rated fuel filter is always required before the carburetor or fuel injector rail. Other brand pumps offer various flow ratings, and output. It is a good idea to review all data provided on the pump to make sure the unit purchased meets the demands of the application. One of the highest quality and most powerful fuel pumps available are those from Weldon. Weldon provides highly detailed and accurate data on each of their fuel pumps.

A typical gasoline engine uses 0.5 pounds of fuel per hour to make each horsepower. Note: Alcohol and other exotic fuel values are different from gasoline. Gasoline weighs in at approximately 6 pounds per gallon. To calculate fuel consumption, we can begin by busing a simple example. Lets say we have a 400 HP engine (or nitrous system). We will use the following formula to calculate "free flow" fuel requirements:

However, if a pump rated at 33 GPH on a 400 HP engine or 400 HP nitrous system was installed on this application using the above example, the engine would experience severe fuel starvation and your wallet would cringe in pain as it becomes "empty" when various parts or an entire engine requires replacement! WHY?

There are several reasons. However, the main reason concerns the way that pumps are rated. Fuel pumps are rated at "zero" pressure (also known as "free flow"). Rating a pump at zero pressure is useless and a marketing gimminck, because the pump will never operate at zero pressure when it is feeding the engine. As fuel pressure increases, the fuel pump slows down and fuel output is reduced. If using a standard "dead-head" type regulator, the pump on a common carburated application may be forced to produce as little as 25 PSI. At 25 PSI the actual output GPH of the pump is much less than at "free flow" rating.

All of this makes choosing a pump size difficult. You may use the following as a fuel pump "rule of thumb". Additionally, it is a good idea to give your system a bit of safety cushion.

Note: This author/engine builder/racer always runs a fuel pump that is just a bit larger than needed, just for insurance.

These minimum pump sizes assume that the fuel system is equipped with fuel lines and fittings of adequate size and proper installation. If the fuel lines are too small (or if there are a lot of restrictive fittings in the system) a larger pump is often required to satisfy the fuel demand of the engine. The minimum fuel line size (from the pump to the regulator) is dependent upon the horsepower output of the engine (and/or Nitrous system) regardless of the size of the pump.

Use these basic figures as a fuel line sizing standard:

Up to 250 HP = 5/16" or -04 AN

Up to 375 HP = 3/8" or -06 AN

Up to 700 HP = 1/2" or -08 AN

Up to 1000 HP = 5/8" or -10 AN

Up to 1500 HP = 3/4" or -12 AN

If using a return-style regulator, an adequately sized return line from the regulator back to the tank is also required. The size of the return line is dependent on the size of the pump you are using, regardless of the engine's horsepower output. The return line must have limited or NO pressure in it. In most cases, the minimum return line size will match that of the supply line, but a larger return line is often preferred.

Use these ratings to decide your return line sizing based upon fuel pump output:

Up to 45 GPH = 5/16" or -04 AN

Up to 90 GPH = 3/8" or -06 AN

Up to 250 GPH = 1/2" or -08 AN

Up to 450 GPH = 5/8" or -10 AN

Mounting the fuel pump also takes some thought and planning. The fuel pump must be mounted as low as possible and as close to the fuel cell (or tank) as possible. DO NOT mount the pump above the fuel tank. However, the type of fuel pump needs to be taken into account here. Gerotor style pumps provide little to no initial suction, and are push-only style pumps. Mounting a gerotor pump at a location that does not provide gravity-fed fuel delivery will cause the pump to burn up and fail in short order. Vane style pumps do offer a limited amount of suction. However, the more suction, the less efficent the design of the pump. Follow the pump manufacturer's installation instructions on mounting location, but keep the above facts in mind when planning the most effective and safe mounting location.

NOTE: We are asked regularly about the actual angle of mounting the pump. The question typically addressed whether the pump must be mounted upright. Take it this way, if the seals in the pump happen to fail, would you want fuel leaking into an electric motor or simply onto the ground?

Mount the fuel pressure regulator as close to the engine as possible. DO NOT use restrictive fittings, especially sharp 90º or "T" fittings. If you must use a 90º or "T" fitting, use the tube style fittings from Earl's, Russell, Goodridge, and others. See Below ...

Of course the fitting at left is what we want to use for uptimum flow and minimal restriction. The inherent restriction of the fittings at right can be hazardous to our race engines and affect the consistent ability to win races. The image at left is an example of a typical full-flow fuel fitting, while the image at right is a very restrictive brass fitting.

The restrictions caused by improper plumbing of a fuel system can cause adverse and costly effects. Years ago race teams copied technology from the aerospace industry (as they tend to do regularly) in using stainless steel braided fuel lines and AN (Army Navy) fittings, including full-flow screw together hose ends and adapters that drastically reduced common fuel line restrictions. Removing fuel flow restrictions and turbulence provided the ability to use smaller, lighter, and more efficient fuel pumps. Engines were able to make more horsepower throughout the RPM range, were more consistent, and lasted longer. The braided lines resisted wear, heat, and compression, and the hose ends reduced turbulence while providing added safety, and ease of installation and removal. The AN hose ends and adapters were manufactured to provide bends and connections that were previously a plumbing nightmare.

Regulators and the Benefits of Return-Style Systems:

One of the biggest restrictions in most modern fuel systems is the "dead-head' regulator. Dead-head regulators are popular because a return line is not required. However, they are not only more restrictive but also create several other problems that can be eliminated with a return-style regulator. Dead-head regulators also have a higher failure rate than return-style regulators.

Mallory, Weldon, and other fuel component manufacturers offer both dead-head and return-style regulators. Base the regulator selection upon system demands and racing class requirements. Dead-head regulators regulate pressure by starting and stopping flow. Return regulators regulate pressure by sending excess fuel back to the tank in a continuous cycle. If confused about the proper regulator choice, think of this simple analogy of a dead-head regulator's operation:

Do you remember as a child, running around the house chasing a sibling or a friend? What happened when you chased them to a room and as they tried to keep you out by trying to close the door. However, they did not quite get the door al the way closed because you were applying pressure against the door? They are pushing, you are pushing, the door is only open a few inches, and then the person on the other side of the door lets go and moves out of the way. Remember stumbling across the floor trying to catch your balance and not destroy furniture or plant your face on the floor? A dead-head regulator is similarly doing the same thing, with the fuel being the object pushing, and the regulator holding the door and then periodically jumping out of the way.

Because a dead-head regulator starts and stops flow, fuel pressure between the pump at regulator is higher than the pressure between the regulator and the carb. This is different on many fuel injected applications, where the regulator is positioned after the fuel rail so that all of the injectors see maximum pressure and flow. However, if the fuel pressure gets too high, it can and will damage the fuel pump. Therefore, the pressure coming out of the pump is limited in many pump designs by a device built into the pump called a pressure bypass. Low pressure pumps are limited to less than 9 PSI and should not be used with dead-head regulators. High pressure pumps for carbureted applications are limited to a pressure between 10 and 25 PSI.

Not only can the fuel pumps used with dead head regulators fail because of pressure issues, but pumps with dead head regulators also run hotter do not last as long as those connected to to a return-style system because it is the fuel that cools the pump. Pounding of the fuel because it can not move freely creates more heat. Fuels pumps working against a dead head regulator will also sound louder during operation.

The Mallory 70 and 110 pumps are low pressure pumps that can be used without a regulator for the street or with a dead head regulator for racing. Mallory 140 and 250 series pumps are both high pressure and high volume pumps, and must be used with some type of regulator, either dead-head or return-style.

It is possible for the bypass in the pump to malfunction. This can cause the pressure to drop or increase to a point that causes the pump motor to fail. Even if the bypass in the pump is working correctly, it is still possible to have a pressure drop with a dead-head regulator, including use with a large pump. See the image below:

Let's say that at idle, gauge #1 will read 10 PSI and gauge #2 will read 8 PSI. At full throttle, the increase in fuel flow will create a pressure drop between the pump and the regulator. The amount of pressure drop depends on the restriction in the fuel line. A 4 PSI drop is not uncommon. Gauge #1 will now read 6 PSI and because a dead-head regulator cannot raise the pressure, gauge #2 will also now read at 6 PSI. The result is a 2 PSI pressure drop at the carburetor or Nitrous solenoids even though a very large pump may be in use.

NOTE: When using a dead-head regulator, a second gauge should be installed just before the regulator. This will allow you to monitor the pressure before the regulator and ensure that it stays higher than the set pressure.

Many race pumps have the bypass set very high (14-25 PSI) to avoid this problem. However, this creates another problem. The higher bypass pressure makes the pump work harder and draw more amperage. In fact, the pump works just as hard at idle as it does at full throttle down the track! This is one of the main causes of early pump failure. To counteract this problem of high amperage draw, some companies manufacture voltage reducers for street cars to slow the pump down and increase the life of the pump. The problem here is that reducing the voltage also has a negative affect on the pump motor.

There is a profound point to be made when I (or your engine builder, carb builder, or fuel pump manufacturer) tell you to run ONLY a return-style system on your vehicles.

Avoid problematic headaches (such as when the pump dies just before a final-round elimination and there isn't enough time on a hot-lap, or for that matter having a spare pump, to fix the problem in time for the next race. Loss By Default because the dead-head regulator helped shorten the life expectancy of the fuel pump.

The bypass in the pump is plugged or disabled when you run a return-style regulator so there is no chance of that component failing.

The pressure just before and after the pump is always the same so there is no need for two gauges. Lighter weight, and less things to monitor.

The return regulator has complete control over the pump pressure and will automatically compensate for pressure drop in the fuel line.

See Explanation Below:

If there is s 2 PSI pressure drop between the pump and the regulator, the return-style regulator will allow the pump to produce 10 PSI. If there is s 4 PSI drop, the pump will be allowed to produce 12 PSI. In either case, the pressure at the regulator will remain at 8 PSI (or whatever you set it at). The pump will also live longer since it is only producing 10-12 PSI instead of 14-25 PSI. This means that a voltage reducer is not needed, even on a street car.

Fuel pressure regulators often suffer from a situation called "recovery time". Recovery time is explained as the amount of time it takes the regulator to react to changes such as a sudden increase in fuel demand (for example when we smash down the throttle or hit the Nitrous button). Return regulators react much quicker for several reasons. Return regulators allow the fuel to flow straight through without making a 90° turn and pounding up gainst that closed door. With a return regulator the fuel doesn't have to make its way around the plunger like it does in a dead-head regulator. Just before we jump on the throttle (or hit the nitrous button), the fuel in a dead head system is barely moving. In a return system, the fuel is constantly moving from the rear of the car to the front and back again. This means that the fuel already has momentum, which reduces recovery time. This movement of the fuel also keeps the pump cooler and reduces vapor lock.

"We never race at any hot or humid tracks in the heat of summer, do we?" {sarcasm}

Dead-head regulators can also cause what is known as "creep", which means the fuel pressure tends to slowly increase. Return regulators cannot creep if setup properly and using the correct size return line.

Accurate fuel pressure regulator adjustment is only acheived when the fuel is flowing through the regulator. Therefore, the engine must be running to adjust the pressure accurately at the carburetor or injectors. The same is true for a Nitrous system. Does anoyone want to make a "guess" that the fuel system presure is set properly the first time the nitrous button is depressed? Adjusting the regulator while the nitrous system is on is tricky at best. Adjustment of return regulators can occur with or without the engine or nitrous system operating. Turn on the pump and set the pressure---simple as that!

One issue that can make a return-style system operate poorly is too much restriction in the return line. To determine is any restriction exists in the return line, turn the pump on (with the engine or Nitrous off) and back the adjustment screw nearly all the way out. Now check the pressure gauge. Less than 3 PSI should show on the gauge (the lower the pressure the better). If more than 3 PSI exists, efforts must be made to reduce the restriction in the return line. This usually entails free-flow fittings at the least, and in many cases a larger diameter return line. Note: a pressure gauge could also be installed in the return line to monitor return pressure.

Nitrous systems are very sensitive to fuel pressure and volume fluctuations. Serious engine damage can occur when the fuel system on a nitrous application is not 100% perfect. It is highly recommended to run two independent fuel systems when using Nitrous (preferably with return-style pump/regulators). Two small systems with small pumps, fuel lines and regulators are usually cheaper than one large system anyway. if forced to use a single, large system, use a return-style pump (return at the pump back to the tank) with two dead-head regulators installed in parallel, not in series. and NEVER use two regulators series in a system with a return-style regulator! Any fuel system with a return regulator must have only one regulator (per system).